In many cases, solenoid valves are an essential component of hydraulic systems. When current is supplied to the electrical conductor, this produces a magnetic field that acts on the armature, exerting a force on it and causing it to move. Because the armature and valve element are connected, the valve element also moves in corresponding fashion, making it possible to control a flow of hydraulic fluid through the flow opening. In many applications, the reaction time, i.e. the time that elapses between an activation signal and a reaction of the hydraulic system, is of critical importance. For example, in automotive engineering, clutches are often actuated by hydraulic systems. The handling of a vehicle depends on the actuation dynamics of the clutch and therefore on the reaction speed of the hydraulic system actuating the clutch. The ability to permissibly influence the handling of the vehicle even in critical situations requires quickly and precisely reacting solenoid valves of the type described at the outset.
A particular class of solenoid valves has a hydraulic fluid-filled valve chamber that accommodates the armature and communicates fluidically with the hydraulic system so that the armature is supported in movable fashion in the hydraulic fluid of the hydraulic system. In this type of solenoid valves with an armature “floating” in hydraulic fluid, the armature displaces the hydraulic fluid in the valve chamber with each switching action. In other words, the armature moves in the fluid, causing a flowing motion of the hydraulic fluid. The flow resistance of the hydraulic fluid acting in opposition to the armature depends, among other things, on its viscosity. With a high viscosity of the hydraulic fluid, the movement of the armature when the solenoid valve is activated is slowed more forcefully than with a low viscosity of the hydraulic fluid. A high viscosity of the hydraulic fluid therefore has a negative impact on the switching dynamics of the solenoid valve and thus on the switching dynamics of the whole hydraulic system. Situations of this kind arise particularly when the hydraulic fluid is cold, for example when a motor vehicle is started.